Semiconductor Device

ABSTRACT

A semiconductor device includes a semiconductor substrate, an nMISFET formed on the substrate, the nMISFET including a first dielectric formed on the substrate and a first metal gate electrode formed on the first dielectric and formed of one metal element selected from Ti, Zr, Hf, Ta, Sc, Y, a lanthanoide and actinide series and of one selected from boride, silicide and germanide compounds of the one metal element, and a pMISFET formed on the substrate, the pMISFET including a second dielectric formed on the substrate and a second metal gate electrode formed on the second dielectric and made of the same material as that of the first metal gate electrode, at least a portion of the second dielectric facing the second metal gate electrode being made of an insulating material different from that of at least a portion of the first dielectric facing the first metal gate electrode.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority fromprior Japanese Patent Application No. 2005-036575, filed Feb. 14, 2005,the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a semiconductor device, and moreparticularly to a structure of a CMIS semiconductor device using a metalgate electrode.

2. Description of the Related Art

As miniaturization of MISFETs progresses to improve integration andperformance of semiconductor devices, it is necessary to reduce athickness of a gate dielectric (insulating film). However, in acomplementary metal-insulator-semiconductor (CMIS) device in which gatelength is 50 nm or less, performance improvement is no longer achievedwhen a conventional polysilicon gate electrode is used. This is becausethe equivalent SiO₂ thickness of the gate dielectric is 2 nm or less inthis technical generation and a reduction of gate capacitance becomesobvious due to interfacial depletion of the polysilicon gate electrode.The depletion of the gate electrode is reduced by increasing chargedensity of the electrode, but the impurity concentration in Si is about2×10²⁰ cm⁻³ at the maximum, and a capacitance reduction corresponding to0.5 nm in the equivalent SiO₂ thickness is also caused in this case.This capacitance reduction will be a serious problem in a CMIS techniquegeneration in which the dielectric thickness is 2 nm or less.

Thus, attention is focused on a metal gate technique using a metal as agate electrode material. Since the metal has high charge densitysubstantially equal to the atomic density, the depletion of the metalgate electrode can be neglected when metal is used as the gateelectrode. For the above reasons, it is considered that the introductionof the metal gate electrode will be essential in the CMIS device in thefuture.

In order to achieve a low threshold voltage in the CMIS device using themetal gate electrode, the work function of the metal which is the gateelectrode needs to be about 3.9 to 4.4 eV in an nMISFET and about 4.7 to5.2 eV in a pMISFET.

Heretofore, means for satisfying this condition has generally been amethod which uses different metals for the nMISFET and the pMISFET, andit has been reported that Ti, Ta, TaSiN, Al and the like have a workfunction suited to the nMISFET and that Mo, Ni, Pt, Ru, RuO₂, IrO₂,TiAlN, TaAlN and the like have a work function suited to the pMISFET(e.g., refer to V. Narayanan VLSI 2004 192 or S. B. Samavedam et at.,IEDM 2002 433).

However, when the gate electrodes of the nMISFET and the pMISFET areformed of different metals, it is necessary to individually produce thegate electrodes, which causes the problem that the manufacturing processis complicated and manufacturing costs increase.

At present, methods of individually producing the gate electrodes in annMISFET and pMISFET include solid phase diffusion, ion implantation,alloying, and total silicidation. However, there are few combinations ofmetals which can be formed by these methods and which satisfy an optimumcondition for the work function of the nMISFET and the pMISFET describedabove, and in the present circumstances, no metal gate technique isestablished which facilitates integration in terms of the manufacturingprocess.

As described above, the gate electrodes of an nMISFET and pMISFET havebeen formed of different metals in order to introduce the metal gatetechnique which will be essential in the future, and therefore, therehas heretofore been the problem that the manufacturing process iscomplicated. Thus, it has been desired to realize a CMIS semiconductordevice which has the same metal gate for an nMISFET and pMISFET andwhich makes integration easy.

BRIEF SUMMARY OF THE INVENTION

According to a first aspect of the invention, there is provided asemiconductor device which comprises:

a semiconductor substrate;

an nMISFET formed on the semiconductor substrate, the nMISFET includinga first dielectric formed on the semiconductor substrate and a firstmetal gate electrode formed on the first dielectric, the first metalelectrode being formed of one metal element selected from the groupconsisting of Ti, Zr, Hf, Ta, Sc, Y, a lanthanoide series, and aactinide series and of one selected from the group consisting of boride,silicide and germanide compounds of the one metal element; and

a pMISFET formed on the semiconductor substrate, the pMISFET including asecond dielectric formed on the semiconductor substrate and a secondmetal gate electrode formed on the second dielectric and made of thesame material as that of the first metal gate electrode, at least aportion of the second dielectric facing the second metal gate electrodebeing made of an insulating material different from that of at least aportion of the first dielectric facing the first metal gate electrode.

According to a second aspect of the invention, there is provided asemiconductor device which comprises:

a semiconductor substrate;

an nMISFET formed on the semiconductor substrate, the nMISFET includinga first dielectric formed on the semiconductor substrate and a firstmetal gate electrode formed on the first dielectric; and

a pMISFET formed on the semiconductor substrate, the pMISFET including asecond dielectric formed on the semiconductor substrate and a secondmetal gate electrode formed on the second dielectric and made of thesame material as that of the first metal gate electrode, at least aportion of the second dielectric facing the second metal gate electrodebeing made of an insulating material different from that of at least aportion of the first dielectric facing the first metal gate electrode,

wherein a relation:(X _(B) —X _(A))×(d _(A) +d _(B))≧3.9is satisfied by electronegativity (X_(A)) and an atomic radius (d_(A), aunit thereof is Å) of a metal element constituting the first metal gateelectrode and the second metal gate electrode and by electronegativity(X_(B)) and an atomic radius (d_(B)) of an element having the highestbinding energy to combine with the metal element constituting the secondmetal electrode among elements constituting the portion of the seconddielectric of the pMISFET facing the second metal electrode.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 is a sectional view of a semiconductor device according to afirst embodiment of the present invention;

FIG. 2 is a graph showing an effective work function on HfSiON and SiO₂of a metal gate electrode;

FIG. 3 is an energy band diagram when a dipole is formed at an interfacebetween the gate electrode and a gate dielectric;

FIG. 4 is a graph showing an effective work function of a Ta simplesubstance and Ta compounds on HfSiON and SiO₂;

FIG. 5 is a graph to explain electronegativity dependency of a compoundpartner relative to a difference of the effective work function of theTa compounds on HfSiON and SiO₂;

FIG. 6 is an energy band diagram when the dipole is formed at theinterface between the gate electrode and the gate dielectric;

FIG. 7 is a sectional view of a semiconductor device according to asecond embodiment of the present invention;

FIG. 8 is a schematic enlarged sectional view of a pMISFET in thesemiconductor device according to the second embodiment;

FIG. 9 is a schematic enlarged sectional view of an nMISFET in thesemiconductor device according to the second embodiment;

FIGS. 10 to 13 are sectional views showing stepwise a manufacturingprocess of the semiconductor device according to the second embodiment;

FIG. 14 is a sectional view of a semiconductor device according to athird embodiment of the present invention;

FIG. 15 is a schematic enlarged sectional view of a pMISFET in thesemiconductor device according to the third embodiment; and

FIG. 16 is a schematic enlarged sectional view of an nMISFET in thesemiconductor device according to the third embodiment.

DETAILED DESCRIPTION OF THE INVENTION

According to embodiments of the present invention described from now on,it is possible to realize a dual work function CMIS semiconductor deviceusing the same metal gate electrode for a pMISFET and an nMISFET.Further, as compared with a case where different metals are used for thepMISFET and the nMISFET, it is not necessary to individually produce thegate electrodes for the pMISFET and the nMISFET, and gate processingsteps are simplified, thereby making it possible to realize the CMISsemiconductor device using a metal gate and making integration easy.

The embodiments of the present invention will hereinafter be describedwith reference to the drawings.

First Embodiment

FIG. 1 is a sectional view of a semiconductor device according to afirst embodiment of the present invention. In a surface region of an Sisubstrate as a semiconductor substrate, there are provided an n-typesemiconductor region 4 and a p-type semiconductor region 5, and apMISFET and an nMISFET are formed in the respective regions. The n-type,p-type semiconductor regions 4, 5 are formed as so-called wells.

On a surface of the n-type semiconductor region 4, a gate dielectric(insulating film) is formed which is made of an oxide 10 containing ametal atom having lower binding energy to combine with a metal atom of agate electrode 8 than Al, Si and Ge. The metal atoms are, for example,Zr, Hf, Ti, Ta, Nb, V, Sc, Y, and a lanthanoide and actinide series.

On a surface of the p-type semiconductor region 5, a dielectric 9different from the gate dielectric 10 is formed which includes any oneof Al, Si and Ge having high binding energy to combine with the metalatoms of the gate electrode 8. The gate dielectric 9 is, for example,AlN, AlON, Al₂O₃, SiO₂, Sin, SiON, HfSiON, GeO₂, or GeON.

On the gate dielectric 9 and the gate dielectric 10, the gate electrode8 is formed which is made of any one of Ti, Zr, Hf, Ta, Sc, Y and alanthanoide and actinide series or a boride, silicide or germanidecompound of these metals. A refractory metal such as W or the like mayfurther be formed on the gate electrode 8. It is to be noted that anisolation region 7, a source/drain region 2, an extension region 3 and asidewall dielectric 6 which are other components in FIG. 1 can be formedin an ordinary semiconductor process.

FIG. 2 shows an effective work function φmeff of the metal gateelectrode when HfSiON which is a high-k dielectric is used as the gatedielectric 10 and SiO₂ is used as the gate dielectric 9.

The metal gate electrode is made of any one of ErGe_(X) (0≦x≦1), LaB₆,Ta and TaB. In all the metal electrodes, an effective work function ofabout 4 to 4.5 eV suited to the nMISFET is shown on SiO₂, and aneffective work function of about 4.7 to 4.8 eV suited to the pMISFET isshown on HfSiON. That is, in accordance with this combination ofmaterials, it is possible to realize a dual-work function CMIS using asingle metal as the gate electrode.

A phenomenon in which the effective work function of the metal electrodethus varies depending on the kind of gate dielectric occurs due to thefollowing reasons: the atom in the dielectric combines with the atom inthe metal electrode at an interface between the metal electrode and thedielectric, and the effective work function is modulated by a dipoleformed due to a difference of electronegativities in the respectiveatoms.

A principle of this will be explained below when the metal electrode isTa by way of example. Ta and Hf have low binding energy and are thusdifficult to create a bond. This is also obvious from that fact that nostable compound of Ta and Hf exists. On the other hand, Ta and O havehigh binding energy and are thus easier to create a bond than thecombination of Ta and Hf. Thus, when the dielectric immediately underthe metal electrode is an Hf-based oxide, a bond of Ta (M) in the metalelectrode and O in the gate dielectric as shown in FIG. 3 is predominantat the interface between the metal gate electrode and the dielectric.Since Pauling's electronegativities of Ta and O are 1.5 and 3.5,respectively, a dipole δ+/δ− is formed at the interface between themetal gate electrode and the dielectric. When the atom on the dielectricside has higher electronegativity than that of the atom on the metalelectrode side among the atoms which create bonds at the interface, theeffective work function is modulated by the dipole to increase as shownin an energy bond diagram of FIG. 3. Therefore, the effective workfunction of Ta increases on an Hf oxide.

On the other hand, because the binding energy of Si and Ta is higherthan that of Hf and Ta, a lot of bonds are created between Ta atoms inthe electrode and Si atoms in the dielectric at the interface betweenthe metal electrode and the dielectric, when the dielectric immediatelyunder the metal electrode is SiO₂. Therefore, the bonds of Ta and Odecrease as compared with a case where the dielectric is HfSiON. SincePauling's electronegativities of Ta and Si are 1.5 and 1.8,respectively, the effective work function is again modulated toincrease. However, the difference of electronegativity here is 0.3,which is lower than in the case of Ta and O having an electronegativitydifference as high as 2.0. Thus, Ta maintains a work function intrinsicthereto on SiO₂, as compared with that on the Hf-based oxide. In thisway, the effective work function of Ta varies on the Hf oxide and onSiO₂.

A difference in the effective work function dependent on the kind ofdielectric which is caused by the dipole formed at the interface betweenthe dielectric and the metal gate electrode is greater when theelectronegativity of the metal atom of the electrode is lower. This isbecause when the electronegativity of the metal atom of the electrode islower, the difference of the electronegativity between the metal atomand O or Si which combines with the metal atom becomes larger. If theyare equally easy to achieve a covalent bond, the binding energy ishigher with a larger difference in the electronegativity, and a bond iseasily created. That is, when the electronegativity of the metal atom ofthe electrode is lower, the number of bonds formed at the interfacebetween the metal electrode and the dielectric is greater, and aninfluence on the effective work function exerted by the dipole isgreater. This is also apparent from that fact that a difference of theelectronegativities on the Hf oxide and on SiO₂ is greater in a compoundof La and Er which has a lower Pauling's electronegativity of 1.1, ascompared with a difference of the electronegativities on the Hf oxideand on SiO₂ in Ta and a Ta compound with a Pauling's electronegativityof 1.5 in FIG. 2.

Furthermore, an advantage according to the embodiment of the presentinvention is provided by a large increase in the work function of themetal gate electrode on the pMISFET side. Therefore, the metal used forthe gate electrode must originally have a low work function suitable forthe nMISFET. That is, the metal used for the gate electrode 8 may be anymetal as long as it has the low electronegativity and work function.Thus, the metal used for the gate electrode 8 is not limited to Ta, La,Er shown in FIG. 2, and may be any one of Zr, Hf, Ti, Ta, Sc, Y, Sc, Yand a lanthanoide and actinide sactinide series.

Moreover, the material of the gate electrode 8 is not limited to a metalsimple substance such as Zr, Hf, Ti, Ta, Sc, Y, and the lanthanoide andactinide series, and may be a compound thereof. The metal compound hassufficiently high electron density, and can solve the problem ofdepletion of the gate electrode interface in the same manner as themetal simple substance.

Further, in general, a compound is chemically stable as compared withthe metal simple substance and has a high melting point, so that it cansuppress a reaction between the metal gate electrode and the dielectricand improve heat resisting properties. However, a compound partner islimited in respect of electronegativity and work function.

FIG. 4 shows the effective work function φmeff of Ta, TaB, TaN and TaCon HfSiON which is a high-k dielectric and on SiO₂. FIG. 5 shows theelectronegativity dependency of the compound partner relative to thedifference of the effective work function of the Ta compounds on HfSiONand SiO₂.

As understood from FIG. 4, TaN and TaC also have values of the effectivework function of about 4.8 eV on SiO₂, and can not obtain a valuesubstantially equal to that of the work function of a polysiliconelectrode for an nMOSFET.

Furthermore, it is apparent from FIG. 5 that the difference in theeffective work function dependent on the kind of dielectric is smallerwhen the electronegativity of the compound partner is higher. This isbecause the compound partner on the gate electrode side which has higherelectronegativity than a metal atom in the dielectric combines with themetal atom in the dielectric at the interface to form a dipole δ−/δ+ asshown in FIG. 6 reverse to the dipole shown in FIG. 3. Its influence isnaturally more obvious when the electronegativity of the compoundpartner is higher. As shown in FIG. 6, since the dipole reverse to thatin FIG. 3 has an effect of decreasing the work function of the gateelectrode, the effects of both dipoles are offset, with the result thatan effect of the work function modulation by the dipole is reduced. Thatis, any compound partner may be used as long as it maintains the workfunction of the metal simple substance to a certain degree and has acertain low degree of electronegativity, and the kinds of compoundsinclude boride, silicide and germanide.

As described above, the effective work function varies depending on thekind of dielectric due to the fact that a difference between theelectronegativity of the metal atom of the gate electrode and theelectronegativity of the atom on the dielectric side which combines withthe metal atom varies regarding the nMISFET and the pMISFET. That is,when the metal atom of the gate electrode is the same, the difference ofthe effective work function of the gate electrode between the nMISFETand the pMISFET is greater if the electronegativity of the atom on thedielectric side which combines with the metal atom varies more greatlyregarding the nMISFET and the pMISFET. O on the dielectric side mainlycombines with metal atom of the electrode at the interface between themetal electrode and the dielectric of the pMISFET regardless of the kindof metal atom in the dielectric as long as the dielectric satisfies acondition for the gate dielectric 10. Thus, the atom on the dielectricside which combines with the metal atom of the electrode in the nMISFETdesirably has electronegativity which greatly differs from that of O,that is, a low electronegativity. This means that when theelectronegativity of the atom on the dielectric side which combines withthe metal atom of the electrode in the nMISFET is lower, the effectivework function of the metal electrode does not increase in the nMISFETand an original low work function is maintained.

From what has been described above, it is desired that an insulatorcontaining the atom with high binding energy to combine with the metalatom of the gate electrode be on the gate electrode side (the gatedielectric 9) of the gate dielectric in the nMISFET, and an oxidecontaining the atom with low binding energy to combine with the metalatom of the gate electrode be on the gate electrode side of the gatedielectric in the pMISFET. As described above, the effect of this ishigher when the electronegativity is lower with regard to the atom whichis in the gate electrode side (the gate dielectric 9) of the gatedielectric in the nMISFET and which combines with the metal atom of thegate electrode. Consequently, the dielectric 9 is not limited to SiO₂used in the example shown in FIG. 2, and may be any one of insulatorscontaining Al, Si and Ge, such as AlN, AlON, Al₂O₃, SiO₂, SiN, SiON,GeO₂ or GeON. The gate dielectric 10 is not limited to the Hf oxide usedin the example shown in FIG. 2 either, and may be any one of oxidescontaining at least one atom having lower binding energy to combine withthe metal atoms of the gate electrode than Al, Si and Ge, such as Zr,Hf, Ti, Ta, Nb, V, Sc, Y and the lanthanoide and actinide series.

Furthermore, as described above, the degree of the effects according tothe embodiment of the present invention is decided by a balance betweenthe work functions and electronegativities of elements constituting thegate electrode and the gate dielectric. That is, the kind of dielectricwhich can provide the effects according to the embodiment of the presentinvention varies depending on the kind of the gate electrode materialand on the kind of the other dielectric, and the material can besuitably selected without departing from the spirit of the presentinvention.

For example, HfSiON used as the gate dielectric in the pMISFET in theexample of FIG. 2 contains both Hf having low binding energy to combinewith the metal atoms of the gate electrode and Si having high bindingenergy to combine with the metal atoms of the gate electrode, andtherefore satisfies both conditions for the gate dielectric 9 and thegate dielectric 10. In the example shown in FIG. 2, the kind of theother dielectric is SiO₂ that does not at all contain Zr, Hf, Ti, Ta,Nb, V, Sc, Y and the lanthanoide and actinide series, which is anecessary condition for the gate dielectric 10. Therefore, it hasrelatively higher effective work function on HfSiON, and HfSiONfunctions as the dielectric of the pMISFET. That is, when the kind ofthe other dielectric is one such as HfO₂ that does not at all containAl, Si and Ge which is a necessary condition for the gate dielectric 9,the effective work function on HfSiON is relatively low, and HfSiONfunctions as the dielectric of the nMISFET. At this time, an increasebreadth of the effective work function of the nMISFET is larger ascompared with a case where the dielectric is SiO₂, but a combination ofsuch dielectrics is effective when the electrode material having workfunction lower than the ideal effective work function where there is noinfluence of dipole is used as the gate electrode.

As described above in detail, the satisfactory advantage according tothe embodiment of the present invention can be provided when: thedielectric of at least the pMISFET is an oxide; there is a differencebetween atomic density of Zr, Hf, Ti, Ta, Nb, V, Sc, Y and thelanthanoide and actinide series contained in the dielectric of thepMISFET, and atomic density of Zr, Hf, Ti, Ta, Nb, V, Sc, Y and thelanthanoide and actinide series contained in the dielectric of thenMISFET; and a magnitude relation of the atomic densities is reverse tothat of atomic densities of Al, Si and Ge between the pMISFET and thenMISFET. This is because in a case of a combination of the dielectricssatisfying such a condition, the fact that the atomic density of Zr, Hf,Ti, Ta, Nb, V, Sc, Y and the lanthanoide and actinide series is highmeans that the atomic density of Al, Si and Ge is low, so that morebonds of the electrode metal atom and O which have large difference inthe electronegativity are formed and the effective work functionincreases. The dielectric, in which the atomic density of Zr, Hf, Ti,Ta, Nb, V, Sc, Y and the lanthanoide and actinide series is higher, thatis, the atomic density of Al, Si and Ge is lower, functions as thedielectric of the pMISFET. The dielectric, in which the atomic densityof Zr, Hf, Ti, Ta, Nb, V, Sc, Y and the lanthanoide and actinide seriesis lower, that is, the atomic density of Al, Si and Ge is higher,functions as the dielectric of the nMISFET. In this case, in order toobtain a sufficiently high effect, the atomic density of Zr, Hf. Ti, Ta,Nb, V, Sc, Y and the lanthanoide and actinide series contained in thedielectric of the nMISFET is desirably 50% or less of the atomic densityof Zr, Hf, Ti, Ta, Nb, V, Sc, Y and the lanthanoide and actinide seriescontained in the dielectric of the pMISFET.

In this way, the effective work function of the pMISFET and the nMISFETcan be optimized considering not only the difference in the kind ofelements constituting the dielectrics of the pMISFET and the nMISFET butalso the difference in the atomic density therebetween.

The dielectric 9 and the dielectric 10 referred to below include adielectric that satisfies both conditions for the dielectric 9 and thedielectric 10, if the combination of dielectric satisfies theabove-mentioned condition for the difference in the atomic density.

In this manner, a suitable combination of materials is used to form thegate electrode side of the gate dielectric of the pMISFET and thenMISFET (the gate dielectric 10 and 9) and the gate dielectric side ofthe gate electrode (the gate electrode 8), so that even when the gateelectrodes of the pMISFET and the nMISFET are formed of the same metal,it can have different effective work functions suitable for the pMISFETand the nMISFET, and by forming a configuration as shown in FIG. 1, itis possible to realize the dual work function CMIS with a single metalgate electrode.

The advantage of the present invention is provided by the dipole whichis formed in accordance with the difference of the electronegativitieswhen two atoms are bonded at the interface between the gate electrodeand the gate dielectric. When a dipole due to deviation of charges of +qand −q is formed by the atomic bond at the interface between theelectrode and the dielectric and the dipole number is constant, a workfunction variation ΔΦ due to this dipole is expressed as follows:ΔΦ∝qD  (1)wherein D is a sum (Å) of atomic radii of the two bonded atoms. Thedeviation of charges increases with an electronegativity differenceΔ_(X), and consequently, the work function variation ΔΦ is proportionateto a product of the electronegativity difference Δ_(X) and the sum D ofthe atomic radii. Here, Equation (1) can be written as follows:ΔΦ=k×Δ _(X) ×D  (2)wherein it is defined that Δ_(X)=_(X) (the element of the gatedielectric) −X (a metal element of the gate electrode). K is a certaincoefficient.

On the other hand, a metal element (element A) of the electrode 8combines with an element (element B) having the highest binding energyto combine with the element A among elements constituting the dielectric10. That is, it is necessary to consider here the electronegativitydifference between the two elements and the sum of the atomic radiithereof. Accordingly, it is required to know what degree of Δ_(X)×Denables the sufficient work function variation ΔΦ. In the case as shownin FIG. 2 where the metal electrode is Ta, a high effective workfunction of about 4.8 eV is obtained by the dipole formed by bonding ofTa and O. Here, a vacuum work function (work function not influenced bythe dipole) of Ta which we used was 4.25 eV. That is, a work functionvariation of about +0.55 eV is obtained by the dipole. Theelectronegativities of Ta and O are 1.5 and 3.5, respectively, and theatomic radii thereof are 1.43 Å and 0.61 Å, so that if these aresubstituted in Equation (2),0.55=k×2×2.04  (3)and it is therefore possible to obtain a relational expression:ΔΦ=0.13×Δ_(X) ×D  (4)

In general, the work function of the gate electrode of the pMISFET needsto be about 0.4 eV higher than the work function of the gate electrodeof the nMISFET. However, a certain amount of increase in the workfunction is also expected on the nMISFET side, but a combination ofmaterials is selected on the nMISFET side so that the work functionincrease is less than 0.1 eV even if the work function increase is atthe maximum. Therefore, it is desired that a work function variation of+0.5 eV or more be obtained on the pMISFET side.

In this manner, the advantage of the present invention can be providedif(X _(B) −X _(A))×(d _(A) +d _(B))≧0.5/0.13

3.9  (5)is satisfied, wherein X_(A) is the electronegativity of the metalelement (element A) of the electrode 8, and X_(B) is theelectronegativity of the element (element B) having the highest bindingenergy to combine with the element A among the elements constituting thedielectric 10, and the atomic radii of the element A and the element Bare d_(A), d_(B), respectively.

On the other hand, since a minimum value of the work function variationon the pMISFET side is set to +0.5 eV, the advantage of the presentinvention can be provided if an increase in the work function in thenMISFET is less than 0.1 eV. That is, an element (element C) having thehighest binding energy to combine with the metal element (element A) ofthe gate electrode 8 among the elements constituting the dielectric 9 ofthe nMISFET may be any element as long as it satisfies(X _(C) −X _(A))×(d _(A) +d _(C))<0.1/0.13

0.7  (6)wherein X_(C) and d_(C) are the electronegativity and atomic radius ofthe element C, respectively. It is to be noted that the effect of thedipoles is greater when the number of the atoms which combine at theinterface and the number of dipoles are larger, so that it is possibleto control the effective work function modulation by changing the atomicdensity at the interface.

Because the advantage of the present invention is derived from the factthat the effective work function is increased by the dipole formed atthe interface between the gate electrode and the gate dielectric, themetal used for the gate electrode must be originally usable as theelectrode of the nMISFET, and needs to have a low work function of 4.4eV or less.

On the other hand, it is known that the work function Φ is stronglydependent on the electronegativity X and that the relation therebetweenis experientially described as follows:Φ=2.27_(X)+0.34  (7)According to this, if the electronegativity X is 1.78 or less, the workfunction Φ is 4.4 eV or less. Therefore, the electronegativity X of themetal used for the gate electrode is desirably 1.78 or less.

The material of the gate electrode is not limited to the metal simplesubstance, and may be a metal compound. However, the elementsconstituting the compound is restricted in that the work function of thecompound must have a value suitable for the gate electrode of thenMISFET. While the work function of the metal is dependent on itselectronegativity as described above, but the electronegativityX(compound) of a compound A_(m)X_(n) is generally described as follows:X(compound)=^(m+n)√{square root over (X_(A) ^(m) X _(X) ^(n))}  (8)wherein X_(x) is the electronegativity of an element X.

That is, the metal compound may be any compound as long as it satisfiesX(compound)≦1.78  (9)

For example, when the metal electrode as shown in FIG. 2 is TaB, theelectronegativity of B is 2.0, so thatX(compound)=²√{square root over (1.5×2.0)}=1.73and this satisfies Equation (9).

Second Embodiment

FIG. 7 is a sectional view of a semiconductor device according to asecond embodiment of the present invention. FIG. 8 is a schematicenlarged sectional view of an Si substrate, a gate dielectric and a gateelectrode of a pMISFET in the semiconductor device of FIG. 7. A gatedielectric made of an oxide 10 is formed on an n-type Si substrate 4. Agate electrode 8 is formed on the gate dielectric 10. Although notshown, a refractory metal such as W or the like may further be formed onthe gate electrode 8.

FIG. 9 is a schematic enlarged sectional view of an Si substrate, a gatedielectric and a gate electrode of an nMISFET in the semiconductordevice of FIG. 7. A gate dielectric is formed on a p-type Si substrate.The second embodiment is different from the first embodiment in that thegate dielectric has a laminated structure, and a lower layer thereofincludes the oxide 10 on which a dielectric 9 different from the lowerlayer is formed, as understood from FIG. 9. Other configurations aresimilar to those in the first embodiment and are not described indetail.

As described in the first embodiment, since an advantage of theembodiment is caused by a dipole formed at an interface between the gateelectrode and the gate dielectric, a thickness of the gate dielectric 9is not limited, and the gate dielectric 9 may be any gate dielectric aslong as it is one or more monolayers between the metal electrode and theoxide film 10. The dielectric 9 needs to be as thin as possible toreduce a decrease in gate capacitance to the minimum, and moreparticularly, the dielectric 9 is desirably one or more monolayers and 2nm or less.

The gate electrode 8 is formed on the gate dielectric 9. A refractorymetal such as W or the like may further be formed on the gate electrode8.

A method of manufacturing the semiconductor device according to thesecond embodiment will next be described referring to FIGS. 10 to 13.First, a region for isolation is formed in an Si substrate 1 by ashallow trench method as shown in FIG. 10, and element formation planregions are separated. Next, the n-type semiconductor region 4 and ap-type semiconductor region 5 are formed, and then the gate dielectric10 is formed on a substrate surface. Subsequently, the gate dielectric 9is selectively deposited only on the gate dielectric 10 on the nMISFETside as shown in FIG. 11. The gate dielectric 9 is desirably as thin aspossible to reduce a decrease in the gate capacitance to the minimum. Amethod of depositing the gate dielectric 9 is not specifically limited,but it is desirable to use, for example, an atomic layer deposition(ALD) method capable of forming a uniform thin film.

Next, the same metal gate material is deposited on the gate dielectric10 and the gate dielectric 9 as shown in FIG. 12, and the gateelectrodes 8 of the nMISFET and pMISFET are simultaneously formed.Methods of the film formation include, for example, a chemical vapordeposition (CVD) method, a vapor deposition method and a sputter method.Subsequently, the gate electrode and the gate dielectric are processedby etching such as lithography and RIE as shown in FIG. 13.

An isolation region 7, a source/drain region 2, an extension region 3and a sidewall dielectric 6 can be formed by properly using an ordinarysemiconductor process after or during the process described above.

In a configuration shown in FIG. 7, the gate electrode is the same forthe nMISFET and the pMISFET, and it is therefore not necessary toindividually produce the gate electrodes unlike conventional gateelectrodes which are different in the pMISFET and the nMISFET. Further,when the gate dielectric 9 may be very thin as in the present structure,gate processing can be performed in one etching step even if the gatedielectric is differently structured in the pMISFET and the nMISFET.Therefore, according to the embodiment of the present invention, it ispossible to manufacture a dual work function CMIS using the metal gateby a simple process.

Furthermore, a transistor in which the gate is formed by means of theprior art where the gate is formed in advance has been described in theabove embodiment, but the present invention is also applicable to atransistor in which the gate is formed by use of so-called damascenemethod considering heat resistance properties of the metal gate.

It is to be noted that the manufacturing method is not described in thefirst embodiment, but the first embodiment is only different from thesecond embodiment in that the gate dielectric is a monolayer, so thatthe first embodiment can be similarly implemented by adapting the gatedielectric formation step in the second embodiment for the monolayer.

The second embodiment described above can provide a similar advantage bya function similar to that in the first embodiment.

Third Embodiment

FIG. 14 is a sectional view of a semiconductor device according to athird embodiment of the present invention. FIG. 15 is a schematicenlarged sectional view of an Si substrate, a gate dielectric and a gateelectrode of a pMISFET in the semiconductor device of FIG. 14. A gatedielectric is formed on an n-type semiconductor region 4. The gatedielectric has a laminated structure, and a lower layer thereof is adielectric 9. A dielectric 10 different from the lower layer is formedon the dielectric 9, and this is different from the first embodiment.

As described in the first embodiment, since a difference in theeffective work function is caused by a dipole formed at an interfacebetween the gate electrode and the gate dielectric, a thickness of thegate dielectric 10 is not limited, and the dielectric 10 may be anydielectric as long as it is one or more monolayers between the metalelectrode and the oxide film 10. The gate dielectric 10 needs to be asthin as possible to reduce a decrease in gate capacitance to theminimum, and more particularly, the dielectric 10 is desirably one ormore monolayers and 2 nm or less. A refractory metal such as W or thelike may further be formed on the gate electrode B.

FIG. 16 is a schematic enlarged sectional view of an Si substrate, agate dielectric and a gate electrode of an nMISFET in the semiconductordevice of FIG. 14. A gate dielectric made of an oxide 9 is formed on ap-type semiconductor region 5. The gate electrode 8 is formed on thegate dielectric 9. A refractory metal such as W or the like may furtherbe formed on the gate electrode 8.

A method of manufacturing the semiconductor device of the thirdembodiment is only different from that in the second embodiment in thata place and a material to form the laminated gate dielectric aredifferent, and the third embodiment can therefore be implemented in thesame manner as the second embodiment. In addition, the semiconductordevice in the third embodiment can provide a similar advantage by afunction similar to those in the first and second embodiments describedabove.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details and representative embodiments shownand described herein. Accordingly, various modifications may be madewithout departing from the spirit or scope of the general inventiveconcept as defined by the appended claims and their equivalents.

1. A semiconductor device comprising: a semiconductor substrate; annMISFET formed on the semiconductor substrate, the nMISFET including afirst dielectric formed on the semiconductor substrate and a first metalgate electrode formed on the first dielectric; and a pMISFET formed onthe semiconductor substrate, the pMISFET including a second dielectricformed on the semiconductor substrate and a second metal gate electrodeformed on the second dielectric and made of the same material as that ofthe first metal gate electrode, at least a portion of the seconddielectric facing the second metal gate electrode being made of aninsulating material different from that of at least a portion of thefirst dielectric facing the first metal gate electrode, and at least theportion of the second dielectric facing the second metal gate electrodebeing formed of an oxide layer of at least one metal element selectedfrom the group consisting of Zr, Hf, Ti, Ta, Nb, V, Sc, Y, a lanthanoideseries and an actinide series.
 2. The semiconductor device according toclaim 1, wherein at least the portion of the first dielectric facing thefirst metal gate electrode is formed of an insulator layer including oneselected from the group consisting of Al, Si and Ge.
 3. Thesemiconductor device according to claim 2, wherein the second dielectricis formed of a single layer of the oxide layer, and the first dielectricis formed of a single layer of the insulator layer.
 4. The semiconductordevice according to claim 1, wherein the first dielectric comprises alaminated structure in which an insulator layer including one selectedfrom the group consisting of Al, Si and Ge is formed on an oxide layerof at least one metal element selected from the group consisting of Zr,Hf, Ti, Ta, Nb, V, Sc, Y, a lanthanoide series and an actinide series.5. The semiconductor device according to claim 4, wherein a thickness ofthe insulator layer of the first dielectric is a thickness of one ormore monolayers and 2 nm or less.
 6. The semiconductor device accordingto claim 1, wherein the second dielectric comprises a laminatedstructure in which the oxide layer is formed on an insulator layerincluding one selected from the group consisting of Al, Si and Ge. 7.The semiconductor device according to claim 6, wherein a thickness ofthe oxide layer of the second dielectric is a thickness of one or moremonolayers and 2 nm or less.
 8. The semiconductor device according toclaim 1, wherein atomic density of the one metal element contained inthe first dielectric is 50% or less of atomic density of the at leastone metal element contained in the second dielectric.
 9. Thesemiconductor device according to claim 1, wherein the semiconductorsubstrate includes a p-type well and an n-type well, and the nMISFET isformed in the p-type well while the pMISFET is formed in the n-typewell.
 10. The semiconductor device according to claim 1, wherein thefirst metal gate electrode is formed of one metal selected from thegroup consisting of Ti, Zr, Hf, Ta, Sc, Y, a lanthanoide series, and anactinide series, or compounds thereof.
 11. The semiconductor deviceaccording to claim 1, wherein a relation:(X _(B) −X _(A))×(d _(A) +d _(B))≧3.9 is satisfied by electronegativity(X_(A)) and an atomic radius (d_(A), a unit thereof is Å) of a metalelement constituting the first metal gate electrode and the second metalgate electrode and by electronegativity (X_(B)) and an atomic radius(d_(B)) of an element having the highest binding energy to combine withthe metal element constituting the second metal gate electrode amongelements constituting the portion of the second dielectric of thepMISFET facing the second metal gate electrode.
 12. The semiconductordevice according to claim 11, wherein a relation:(X _(C) −X _(A))×(d _(A) +d _(C))≦0.7 is satisfied, wherein X_(C) andd_(C) (a unit thereof is Å) are electronegativity and an atomic radiusof an element having the highest binding energy to combine with themetal element constituting the first metal electrode among elementsconstituting the portion of the first dielectric of the nMISFET facingthe first metal electrode.
 13. The semiconductor device according toclaim 12, wherein the electronegativity of the metal element of thefirst metal gate electrode and the second metal electrode is 1.78 orless.
 14. The semiconductor device according to claim 12, wherein thefirst metal gate electrode and the second metal gate electrode are madeof a compound A_(m)X_(n) of a metal element A and another element X, andelectronegativities X_(A) and X_(X) of the metal element A and the metalelement X satisfy a relation:^(m+n) √{square root over (X_(A) ^(m)X_(X) ^(n))}≦1.78
 15. Thesemiconductor device according to claim 1, wherein the first metal gateelectrode and the second metal gate electrode are formed of one selectedfrom the group consisting of Ti and compounds thereof.
 16. Thesemiconductor device according to claim 1, wherein the first metal gateelectrode and the second metal gate electrode are formed of one selectedfrom the group consisting of Ta and compounds thereof.